"We've had trouble with a lot of bloggers," X17 co-owner Brandy Navarre told the Los Angeles Times for a story on its Web site. "But he's the biggest, and the most arrogant and pigheaded about it, frankly.

"He is stealing our images and costing us money every day," she said.

Hilton, whose real name is Mario Lavandeira, said he believes he has done nothing illegal.

"I am going to vigorously defend myself," he said. "I am willing to step up to the plate and fight for my rights and fight for the rights of all bloggers."

His attorney, Bryan Freedman, said Hilton has a legal right to make satirical or humorous use of newsworthy photographs.

If the copyright lawsuit succeeds, "the effect would be to eliminate the ability to comment on and transform photographs under the fair-use exception to the Copyright Act," Freedman said.

But X17's lawyer, John Tehranian, argued that Hilton "is basically free-riding on the labor and efforts of X17 and its photographers who stay up all night and roam the city."

Seven other photo agencies sent Hilton a joint letter demanding that he stop using their photographs but they have not sued, the Times said.